Hi I'm new to all this and I'm have a bit of a problem With my nitrate, can't seem to keep the Levels down. Goes way up everything else fine just nitrates. And I have tried water changes in the last week. I've done 3 of them and still high my nitrate is at 5.0ppm my ammonia is at0ppm hp at 7.8 and nitrite at 0ppm what can I'm be doing wrong.?